1. Field of the Invention
The present invention relates to an antenna device for use in an indoor type radio base station.
2. Description of the Related Art
FIGS. 12A and 12B are illustrations showing the positional configuration of a plurality of flat antennas mounted in a conventional antenna device, wherein FIG. 12A is a front view and FIG. 12B is a side view. FIGS. 13A and 13B are magnified views respectively of the antenna device of FIG. 12A and FIG. 12B showing one of the flat antennas mounted therein, wherein FIG. 13A is a sectional view observed from the line cut along Ixe2x80x94I of FIG. 12A, and FIG. 13B is a plain view of that flat antenna. Further, FIG. 14 is a block diagram showing a configuration of the conventional antenna device.
In these figures, reference numeral 100 denotes a rectangular ground plate, which is fixed along a wall surface within a house and supporting each of the flat antennas, the detail of which is explained later, numerals 101 to 106 are flat antennas which are supplied with electric power, and disposed on the ground plate 100 with a predetermined distance from one another, and numeral 107 denotes a covering stuff, which is 3.0 mm thick and made of a resin material such as ABS resin or the like.
In close proximity to the upper corners of the ground plate 100, a flat antenna 101 and another flat antenna 102, which are used for signal transmission, are disposed at a predetermined distance away from the edge surface of the ground plate 100 so as to prevent reduction of the gains of these flat antennas 101 and 102. On the other hand, in close proximity to the lower corners of the ground plate 100, a flat antenna 103 and another flat antenna 104, which are used for signal reception, are disposed at a predetermined distance away from the edge surface of the ground plate 100 or from each other so as to prevent reduction of the gain of these flat antennas 103 and 104, and also to eliminate the mutual effect on each other. Specially, the flat antennas 103 and 104 provided as the signal reception antennas are disposed at a predetermined distance away from each other for eliminating the mutual effects, in order that they function together as a diversity antenna. Further, flat antennas 106 and 105 are disposed between the flat antennas 101 and 102 and also between the flat antennas 103 and 104 respectively, each as an interference detection antenna for searching for a radio wave that can be an interference for communications of the base station.
Since the flat antennas 101 to 106 have more or less the same configuration except their exact dimensions, the flat antenna 104 is taken up here as an example for explaining the construction thereof.
The flat antenna 104 is schematically composed of, as shown in FIGS. 13A and 13B, a radiation conductor portion 104a disposed in parallel to the surface of the ground plate 100 at a predetermined distance therebetween, a ground conductor portion 104b in contact with the surface of the ground plate 100, and a bent portion 104c connecting these conductor portions 104a and 104b. The radiation conductor portion 104a is configured in such a manner as to be supplied with electric power by way of a supporting member 111 having an RF connector 110, whereas an insulation spacer 112 for maintaining the distance H between the radiation conductor portion 104a and the ground plate 100 is provided at the far end of the radiation conductor portion 104a. The ground conductor portion 104b is fixed to the ground plate 100 in a rather easy way by a rivet 113. Note that only one side of the ground plate 100 is formed with a conductor pattern (not shown).
The length L1 of the radiation conductor portion 104a shown in FIG. 13A is determined in accordance with the frequency that the antenna uses, whereas the length L2 between the bent portion 104c and the power feeding point P is set in such a manner that the impedance becomes 50 ohm. The width W of the ground conductor portion 104b is determined by the gain of the antenna.
As shown in FIG. 14, the flat antennas (TX1) 101 and (TX2) 102 are transmission antennas, which are connected respectively to a first transmitter 120 and a second transmitter 121. The flat antenna (RX1) 103 is connected in a branched manner to a first receiver 123 and also to a third receiver 124 by way of an amplifier (AMP) 122, the flat antenna (RX2) 104 is connected in a branched manner to a second receiver 126 and also to a fourth receiver 127 by way of an amplifier (AMP) 125. The flat antenna (MX1) 105 is connected in a branched manner to the first receiver 123 and the second receiver 126 by way of an element 128 provided with the function of an amplifier and that of a frequency converter, and these first receiver 123 and second receiver 126 are connected to a first signal combiner 129. Further, the flat antenna (MX2) 106 is connected in a branched manner to the third receiver 124 and the fourth receiver 127 by way of an element 130 provided with the function of an amplifier and that of a frequency converter, and these third receiver 124 and fourth receiver 127 are connected to a second signal combiner 131.
In the antenna device configured as mentioned above, the first transmitter 120 and the second transmitter 121 use different frequencies from each other, which are different also from those of the receivers 123, 124, 126 and 127.
The operation of the conventional antenna device is as follows.
First of all, when a signal transmitted from the nearby area of the radio base station (hereinafter may be referred to as a radio station or just as a base station) is received by the flat antenna 105 that is an interference detection antenna, the thus received signal is amplified at the element 128 where a frequency conversion is processed, and thereafter sent to the first receiver 123 and the second receiver 126, wherein if the frequency of the thus received signal is same as that of the signals transmitted from the first transmitter 120 and the second transmitter 121, then the transmission of signals of the corresponding frequencies is prohibited in order to prevent a possible interference.
After the above procedure by use of the interference detection antenna, a signal transmission at a usable frequency is started. In this case, the TDMA (Time Division Multiple Access) communication is enabled by dividing one cycle of a transmitted signal into three portions, and also by allocating one frequency to three communication lines. In this antenna device, two transmitters 120 and 121 are used, wherein if the both frequencies are usable; each transmitter can hold three communication lines, so that communications of 6 lines can be assured in parallel by the whole antenna device. The communication using this time-division method can be applied even in the signal receiving case.
Next, in the case of signal receiving, the same one signal is received simultaneously by two different antennas; namely the flat antennas 103 and 104, and thereafter the thus received signals are amplified by the amplifiers 122 and 125, respectively, and the amplified signals are then fed through the first receiver 123 and the second receiver 126 to a first signal combiner 129 where these signals are combined after synchronizing the phase of each signal. This can be done by use of the diversity technique for improving the strength of signal reception.
It is to be noted here that the radiation pattern made of one flat antenna in the vertical direction is excellent not only about the directivity in the frontward direction, but also that in the upward and downward directions as well, as shown in FIG. 15.
It is also to be noted that since this kind of antenna device is used in a base station 133 mounted at the upper side of an inner wall surface inside a building 132 as shown in FIG. 16, there is a case in which a mobile station a at a nearby area from the base station 133 and another mobile station bat a remote place from the base station 133 make a communication with each other by way of the base station 133.
However, since attenuation of a signal transmitted from the mobile station b becomes greater in proportion to the distance between the mobile station b and the base station 133, the signal transmitted from the mobile station a becomes an interference to the signal transmitted from the mobile station b, so that there has been a problem that the communication quality of the mobile station b is degraded.
The present invention has been proposed to solve the problems aforementioned, and it is an object of the present invention to provide an antenna device which is capable of maintaining the communication quality of a mobile station, which is in a remote place from its base station.
In order to achieve the above object, an antenna device according to a first aspect of the present invention is constructed in such a manner that it comprises: a ground plate uprightly mounted in the vertical direction, one or more than one flat antenna elements disposed on the ground plate for receiving a signal transmitted from a mobile station, and a non-powered short-patch antenna element disposed on the vertically upright ground portion below at least one of the flat antenna elements, Wherein the distance between the uppermost portion of the short-patch antenna element and the uppermost portions of the flat antenna elements is the length of xc2xd wavelength.
An antenna device according to another aspect of the present invention is constructed such that the short-patch antenna element is shared by at least one pair of the flat antenna elements.
An antenna device according to further aspect of the present invention is constructed such that the above one or more than one flat antenna elements are disposed mutually close to each other, and at least a pair of non-powered antenna elements are disposed in such a manner as to vertically extend between the plurality of flat antenna elements.
An antenna device constructed as above further comprises metal fixing elements for fixing the pair of non-powered antenna elements to the ground plate, which metal fixing elements protruding from the non-powered antenna elements in the direction intersecting the direction of the electric field at right angles.
An antenna device according to further aspect of the present invention is constructed such that each of the non-powered antenna elements is formed with a spacer at the respective end portions thereof for suppressing vibrations possibly transmitted from the ground plate, which spacer being made of an electrically insulative material.
An antenna device according to still further aspect of the present invention is constructed such that the metal fixing elements and the ground plate are electrically insulated from each other.
An antenna device according to still further aspect of the present invention is constructed such that the insulation is performed by slits formed in the surface of the ground plate around the respective metal fixing elements.
An antenna device according to yet still further aspect of the present invention is constructed such that the non-powered short-patch antenna is an elongate plate extending along the lowermost edge portion of the ground plate throughout all the range from left to right.